Imaging devices, such as ink jet printers, typically include one or more printheads each having a plurality of ink jets from which drops of ink are ejected towards an image receiving member to form images. The receiving member may be recording media or it may be a rotating intermediate imaging member, such as a print drum or belt. In a printhead, individual piezoelectric, thermal, or acoustic actuators in the ink jets generate mechanical forces that expel ink drops through an ink jet nozzle or orifice in response to an electrical voltage signal, sometimes called a driving signal. The amplitude, or voltage level, of the signals affects the amount of ink ejected in each drop. Images are formed on the receiving member by selectively activating the actuators of the ink jets to eject drops in timed registration with the relative movement of the receiving member with respect to the printhead(s).
The image quality of the images produced by an imaging device is determined in part by the drop mass of the drops generated by the ink jets. Image quality may be degraded if the ink jets of the printheads produce drops having drop mass that is not within specification or if they have inconsistent drop mass from jet to jet, or printhead to printhead. As part of a setup or maintenance routine, the printheads of an imaging device may undergo a normalization or calibration process so that the ink jets of the printheads produce ink drops having substantially uniform drop mass within desired specifications. Normalization of the ink jets of the printheads may be accomplished by modifying the driving signals that are used to activate the actuators of the jets. To enable normalization of the drop mass of the drops produced by the ink jets, the drop mass must first be determined. Knowledge of the drop mass enables calibration of the driving signals for the ink jets so that the ink jets of the printheads produce drops having substantially the same drop mass.
In previously known systems, however, the drop mass of drops emitted by a printhead or printheads of an imaging device was determined by printing onto transparencies and measuring the weight difference before and after the ink is transfixed to the sheets. The weight difference between the printed and non-printed sheets corresponds to the total weight of the ink on the sheet which is then divided by the total number of drops printed onto the sheet to arrive at the average drop mass for the printhead or printheads used to print onto the transparencies. Based on the determined average drop mass using the printed transparencies, the drive signals for actuating the ink jets of the printheads may be calibrated to adjust the drop mass of the drops produced by a printhead to be within specifications. While such a method of determining average drop mass is effective, such techniques are typically only available for use at the factory, not in the field. In addition, it may take several iterations and huge amounts of resources, i.e., time, transparencies, and ink, to calibrate the overall drop mass in a printhead.